The invention relates to a thermal imaging device comprising a slab of ferroelectric or pyroelectric material bearing an infrared permeable common electrode on one main surface and a signal electrode structure on the opposite main surface. The signal electrode structure is electrically connected to electrodes of a circuit substrate by conductors surrounded by a thermally insulating material.
The present invention also provides a method of manufacturing a thermal imaging device. The method comprises the steps of providing a slab of ferroelectric or pyroelectric material with an infrared permeable common electrode on one main surface and with a signal electrode layer on the opposite main surface.
A significant problem with such devices is to provide adequate mechanical support for the slab of ferroelectric material, while at the same time providing good thermal isolation between adjacent sensing regions and between the sensing regions of the device and the circuit substrate. The substrate is, for example, an electronic multiplexer.
U.S. Pat. No. 4,143,269 describes a ferroelectric imaging system in which the conductors are conductor rods which are either in a vacuum (in which case it does not appear that the conductor structure per se will provide adequate mechanical support for the ferroelectric slab), or are embedded in a mass of thermally insulating material (for example, a glass-filled photoresist). When the conductor rods are embedded in such a mass of thermally insulating material, there is still a heat flow between adjacent detector elements in a direction transverse to the longitudinal axes of the conductors. This heat flow impairs the device performance in two ways.
Firstly, there is a degradation of the thermal limits of detection. Thus, the transverse heat conductance provides a significant contribution to the signal produced by a given sensing element. Secondly, the transverse flow of heat can cause thermal crosstalk between adjacent elements.